1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus including the electrophotographic photosensitive member.
2. Description of the Related Art
In recent years, an electrophotographic photosensitive member (organic electrophotographic photosensitive member) including an intermediate layer that contains an inorganic compound and a photosensitive layer that contains a charge generating substance and a charge transporting substance and is disposed on the intermediate layer has been used as an electrophotographic photosensitive member used for electrophotographic apparatuses.
The potential characteristics (chargeability and sensitivity) of the electrophotographic photosensitive member depend on the types of materials used for the intermediate layer and the photosensitive layer. In particular, the potential characteristics of the electrophotographic photosensitive member are significantly dependent on materials such as metal oxide particles, an organic compound, and a binder resin used for the intermediate layer. Thus, the potential characteristics of the electrophotographic photosensitive member can be improved through the structures and combination of the above-described materials.
With a recent increase in the processing speed of electrophotographic apparatuses, in addition to the improvement in potential characteristics such as the increases in chargeability and sensitivity, the potential variation (changes in chargeability and sensitivity) after repeated use needs to be further suppressed. Specifically, the potential variations (changes in chargeability and sensitivity) in terms of (1) and (2) below need to be further suppressed:
(1) Long-term repeated use from the initial use of an electrophotographic photosensitive member to the end of the life of the electrophotographic photosensitive member; and
(2) Relatively short-term repeated use (e.g., from the first image output to the completion of about 1000 continuous outputs).
In view of (1) above, the potential variation may be increased depending on the configuration of the electrophotographic photosensitive member (the potential characteristics may be significantly degraded). In such a case, even if the electrophotographic photosensitive member is left to stand after long-term repeated use, the potential characteristics do not return to the original level, which means low recoverability.
In the case where the potential variation is large in view of (2) above, for example, the color of an image formed on the first output sheet sometimes becomes different from that of an image formed on the 1000th sheet. However, such a short-term potential variation is easily recovered by leaving the electrophotographic photosensitive member so that the potential characteristics return to the original level within a relatively short time.
It is believed that the potential variation of (1) is caused by accumulating the potential variations of (2) that are not recovered within a short time even if the electrophotographic photosensitive member is left to stand.
It is important to suppress the potential variations of (1) and (2) above and thus allow an electrophotographic photosensitive member to always stably output an image. In particular, the potential variation of (2) above is problematic, and the change in color needs to be small in any circumstances.
In other words, the potential variation of (2) above at the beginning of use of an electrophotographic photosensitive member needs to be suppressed, or the potential variation of (2) above after the long-term repeated use of the electrophotographic photosensitive member needs to be suppressed.
Japanese Patent Laid-Open No. 2006-30700 discloses a technology that suppresses a potential variation by providing an acceptor compound (organic compound) to a metal oxide as a material constituting an intermediate layer of an electrophotographic photosensitive member. Japanese Patent Laid-Open No. 2004-219904 discloses a technology that suppresses a potential variation by disposing a dye (organic compound) on the surface of a metal oxide, the dye absorbing light with a wavelength of 450 to 950 nm. However, neither focuses on the potential variation of (2) above.
Japanese Patent Laid-Open No. 09-197701 discloses an intermediate layer including an organic metal compound such as an organic zirconium compound, an electron-accepting compound (organic compound), and a binder resin in a mixed manner. However, the potential variation of (2) is not mentioned.
The electrophotographic photosensitive members disclosed in Japanese Patent Laid-Open No. 2006-30700, Japanese Patent Laid-Open No. 2004-219904, and Japanese Patent Laid-Open No. 09-197701 certainly each had a small potential variation of (2) when used for a short time at the beginning of use of the electrophotographic photosensitive member. However, when a short-term potential variation ((2) above) after the long-term repeated use of the electrophotographic photosensitive member ((1) above) was measured, the potential variation was increased compared with the initially measured potential variation.
Regardless of the degree of potential variation after long-term repeated use, the short-term potential variation after the long-term repeated use was increased compared with the initially measured short-term potential variation.